Survival motor neuron spinal muscular atrophy

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Description:

Survival motor neuron spinal muscular atrophy (Spinal muscular atrophies of childhood) is a term used used to describe certain forms of spinal muscular atrophy (SMA) that are associated with the Survival of Motor Neuron (SMN) protein. These include Werdnig-Hoffmann disease and Kugelberg-Welander disease.

Sometimes the term "spinal muscular atrophy" is used to imply an association with survival motor neuron, but the phrase "spinal muscular atrophy" is also used to refer to unrelated conditions such as Kennedy disease.

The term dates back to at least 1973.

Types

The most common form of SMA is caused by mutation of the SMN gene, and manifests over a wide range of severity affecting infants through adults. This spectrum has been divided into groups, depending on the age of onset, and are as followed:

Causes

In humans and chimps, the region of chromosome 5 that contains the SMN (survival motor neuron) gene has a large duplication. A large sequence that contains several genes occurs twice—i.e. once in each of the adjacent segments. A second change that is found only in humans is that the two copies of the gene—known as SMN1 and SMN2—differ by only a few base pairs. The important change in the SMN2 gene, for the purposes of SMA, is a silent mutation that occurs at...Read More